1. Field of the Invention
The present invention relates in general to digital audio broadcasting, and more specifically, to a method for determining the validity of a lookup table in a radio receiver.
2. Description of the Related Art
With the introduction of digital audio broadcasting, a radio listener has the opportunity to experience a higher quality of broadcast reception utilizing a digital broadcast as opposed to a traditional analog broadcast. Improved reception, better audio quality, and data services are some of the benefits of using digital audio broadcasting.
A duplicative audio broadcast system simultaneously transmits 1) a primary channel having at least a main program content and preferably including a supplemental data stream, and 2) a backup channel with main program content that is at least a partial duplicate of the main program content in the primary channel but usually without the supplemental data stream. Certain differences in the backup channel transmission allow it to be received by a receiver under conditions in which the primary channel is unreceivable.
To receive the full benefits of digital audio broadcasting, listeners must have a digital audio receiver to receive the digital audio broadcast, therefore there will be a transition period as listeners migrate from analog audio receivers to digital audio receivers. During the transition period, if a broadcast station wants to maintain their listening audience, the broadcast station must transmit both a digital broadcast for those listeners who are capable of receiving the digital broadcast and transmit an analog broadcast for those listeners who are still utilizing the analog audio receiver.
A method of broadcasting both the digital signal and the analog signal over a frequency range for a particular audio broadcast station has recently become available. In-Band On Channel (IBOC) is a system that has been adapted to transmit a hybrid signal. IBOC transmits the analog signal on a center portion of the frequency range with the digital signal occupying an upper and lower side portion of the frequency range.
Eventually, hybrid stations may transition to an all digital audio broadcast station while retaining the duplicative nature of the broadcast signal (i.e. both the primary and backup channels are digital). In the all digital duplicative system, the backup channel transmits at a lower effective data rate in order to provide a more robust signal that can be received during times that (or at a place where) the primary channel is impaired. In order to achieve a lower data rate, the supplemental data and possibly some portion of the main program content are omitted from the backup channel (e.g., by encoding the main audio program at a lower bit rate).
An advantage with digital audio broadcasting is that the digital signal contains auxiliary program data, station identification information, or other information in addition to digital audio. The station identification information and auxiliary program data is useful in informing the listener as to the content of the broadcast signal without having to wait to listen to a received broadcast to determine the contents thereafter. The digital signal contains, in part, a plurality of subcarriers each containing digital information representative of program data transmitted by the IBOC station. Information such as station identification (e.g. call letters), song title, artist, genre, and album are some of the information that can be quickly referenced by the listener. However, decoding and outputting the digital signal to the listener may be more timely than decoding and outputting the analog signal due to the complex decoding that is performed on audio and data subcarriers of the digital signal.
A lookup table may be used to quickly obtain information on a broadcast station without having to first receive the information. The lookup table would contain station related information regarding a specific broadcast station such as station identification, genre, broadcast type, station location, station alias name, program format, and other related information that is not dependent upon a song selection currently being broadcast by the IBOC station. The lookup table would be constructed for a respective broadcast region that the receiver has been updated for. The frequency range or channel of the broadcast is used to index the lookup table to retrieve and display the station related information without having to decode the digital signal. A lookup table can be constructed or rebuilt automatically by the receiver or manually by a listener. An example of how the lookup table could be rebuilt is by using a scan function. Once initiated the receiver will scan through a broadcast band looking for digital audio broadcast stations transmitting a digital signal. When the receiver determines that a frequency range or channel is broadcasting a digital signal, the receiver will store the station related information for the digital audio broadcast station at a table entry in the lookup table. Each table entry in the lookup table will be associated with a respective frequency range or channel of a respective digital audio broadcast station. Due to the length of time required for such a full scan, however, it should only be performed infrequently or else a second tuner should be present.
However, if a listener travels out of the broadcast region and is no longer able to receive the IBOC station for the respective broadcast region, the lookup table is no longer valid and gives erroneous data if a second digital station is broadcasting on the same channel in the new geographical region. Furthermore, the listener unaware that the new geographical region has been entered would receive no notification that such an event has taken place and that the lookup table currently stored in memory is invalid.
It would be desirable to provide a method for determining whether a lookup table containing digital audio broadcast information is invalid for a broadcast region so that a receiver does not rely on erroneous data and can notify a listener that the lookup table needs to be rebuilt. Such a method that automatically tracks and verifies the validity of a lookup table would overcome such disadvantages.